The technical field of this disclosure is speed sensors for wheel bearing packages. In particular, a sensor cap is provided with an active sensor chip and associated elements into an integrated, sealed unit that accurately positions the sensor and protects the sensor from harsh conditions.
Speed sensors are commonly included as an element in wheel bearing packages. Prior art sensors include passive sensors. Passive sensors provide a magnetic field with some type of magnet, generally combined in proximity with a sensing coil into a sensor component. The coil-magnet component is usually mounted fixed relative to the vehicle, since it has signal wires leaving it. A variable reluctance ring, generally a toothed iron ring, is mounted so as to turn at the speed of the wheel, within the magnetic field, thereby creating an electric signal that varies with wheel speed.
Passive sensors use wire coils and pole pieces combined with magnets to sense the moving sensor ring teeth. With regard to production of an integrated assembly, the prior sensors have presented some challenges. In particular, variable reluctance sensors include a large number of delicate parts that must be maintained in a connected state during packing in a housing. The fine wire coils and connections between components are particularly fragile. The coils and connections have been known to break easily during over-molding, as a result of thermal stress, during servicing and for other reasons.
It would be desirable to have a sensor system that would overcome the above disadvantages without involving extra steps and expense.
The present invention provides a sensor device and method of manufacturing for sensing a rotating a speed of a vehicle wheel. The device includes a sensor cap or body that mounts an active sensor element and the electrical terminations therefore into an integrated over-molded package with a minimum number of parts. The present invention utilizes a plastic holder, integrated into the cap, that positions the sensor and terminals. The cap includes an annular positioning ring. During molding the active sensor is positioned a predetermined distance with respect to a positioning flange on the positioning ring. When mounted to the hub of a bearing, the positioning ring provides a mounting interface that positions the sensor an operative distance to a sensor wheel.
An aspect of the present invention provides a speed sensor device including a cap portion with a flange portion and a sensor assembly with a body portion and a sensor. The body portion is integrally molded to an inner portion of the cap at a predetermined position to allow a portion of a hub including a tone wheel attached thereto to contact with the flange portion and position the sensor a predetermined distance from the tone wheel.
Other aspects of the invention provide a flange portion formed on an annular mounting ring formed in the cap portion. The body portion can include a lower portion adapted for maintaining the sensor in a predetermined location in the body portion. The lower portion can be a generally cylindrical portion with a locating tab formed thereon for engaging a corresponding groove in the sensor, the tab and groove positioned to maintain the sensor with respect to the body portion in the predetermined location. The lower portion can be a generally cylindrical portion with a locating flat side formed thereon for contacting a corresponding flat side of the sensor, positioned to maintain the sensor with respect to the body portion in the predetermined location.
Other aspects of the invention provide an upper portion of the body portion with a pair of terminals. The upper portion of the body portion can include a pair of retaining catches for retaining the pair of terminals. A capacitor can be electrically connected across the pair of terminals. The capacitor can be housed in a transverse slot located in the upper portion of the body, the transverse slot being located adjacent the pair of terminals. The sensor can be electrically connected to the pair of terminals. The predetermined distance between the sensor and the tone wheel can be about 0.050 inches.
Another aspect of the invention includes a method of manufacturing a speed sensor device including providing a sensor assembly including an insert body, a sensor located in a lower portion of the insert body, a pair of terminals located in an upper portion of the insert body electrically connected to the sensor. A mounting ring can be provided with a locating flange. The sensor assembly and mounting ring can be thermoformed into a cap portion.
Other aspects of the present invention include locating the sensor assembly at a predetermined position in the cap portion. The lower portion of the insert body can include a tooth and the sensor can include a groove, the tooth and groove cooperating to secure the sensor in the predetermined position in the cap portion. The lower portion of the insert body can include a flat surface and the sensor includes a flat portion, the flat surface and the flat portion cooperating to maintain the sensor in the predetermined position in the cap portion. The pair of terminals can be are secured in a pair of retaining catches formed in the upper portion of the insert body. The method can include providing a capacitor electrically connected to the pair of terminals before thermoforming the sensor assembly into the cap portion. The capacitor can be positioned in a slot formed in the upper portion of the insert body. The sensor assembly can be located at the predetermined position in the cap portion by locating the sensor assembly relative to a position of the flange portion.
Another aspect of the present invention provides a speed sensor device for sensing a rotating speed of a vehicle wheel including a thermoplastic sensor body, a mounting ring formed in the sensor body, the mounting ring including a flange portion, a plastic insert integrally molded into the sensor body adjacent the mounting ring, an active sensor element located in a lower end of the plastic insert, a face of the active sensor element being vertically spaced by the lower end of the plastic insert a predetermined distance from the flange portion and a pair of terminals electrically connected to the active sensor element, the pair of terminals extending from an upper end of the plastic insert, wherein the flange portion, when located on a hub associated with the wheel, is adapted to space the active sensor element an operable distance from a tone wheel mounted to the hub.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.